The present invention relates to apparatus and methods for effluent stream analysis and more particularly to apparatus and methods for providing a highly stable and smooth flow of effluent around a measuring electrode.
Polarography, one of a broad class of voltameric techniques, provides chemical analysis of substances in electrolyte solution by the observation of current and voltage relationships of electrodes immersed in the solution. At low voltages, no current flows between the electrodes. However, as the voltage is increased, it becomes great enough for deposition of each reducible substance in solution on the electrodes, and current begins to flow. Generally, the magnitude of the current is proportional to the concentration of the reducible substances in solution and the magnitude of the voltage required to induce this current flow is indicative of the identity of the substance in solution. Thus, precise measurement of the current in the immersed electrodes, as a function of applied potential, provides both qualitative and quantitative analysis of the reducible substances in solution.
Chromatography is a method of separating and analyzing mixtures of chemical substances. A flow of solvent or gas causes the components of the mixtures to migrate differentially in a sorptive media subject to an effluent flow. The time at which the various chemical substances of the mixture emerge from and effluent flow provides an indication of the qualitative content of the substances.
A typical detection apparatus for determining the qualitative content of the substances appearing from the effluent flow may be a form of polarographic detector. Such a polarographic detector consists generally of a variable voltage source, a circuit for measuring current, and an electrolysis cell. The cell typically contains three electrodes immersed in the effluent flow. The three electrodes comprise a reference electrode at which the variable potential is applied, a working or indicating electrode at which current flow is measured, and an auxiliary or counter electrode which regulates the potential between the reference and working electrodes.
The most widely used working or indicating electrode in polarographic detectors is the dropping mercury electrode which consists of a fine bore capillary tube above which a constant head of mercury is maintained. The mercury emerges from the tip of the capillary at the rate of a few milligrams per second and forms spherical droplets at the capillary orifice into the effluent solution at a typical rate of one every two to ten seconds.
The dropping mercury electrode has a number of advantages over other varieties of electrodes. For example, mercury has a high hydrogen overvoltage which allows observation of processes which would normally be obscured by the decomposition of water at other elements. In addition, periodic renewal of the surface area of the dropping mercury electrode minimizes problems due to surface composition changes.
However, the prior art employment of dropping mercury electrodes in liquid chromatographic systems has been severely hampered by (1) an appreciable dead volume existing between the effluent flow and the mercury and (2) by turbulent flow resulting from prior art attempts to minimize the dead volume.
It is accordingly an object of the present invention to provide apparatus and methods for effluent stream analysis wherein the dead volume between the effluent stream and the indicating electrode is minimized. It is a further object of the present invention to provide apparatus and methods for effluent stream analysis wherein a smooth non-turbulent flow is provided around the electrode to maximize sensitivity of analysis.
Additional objects and advantages of the present invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.